Kollision zwischen ASK 18B und ASW 15 nahe Hasenmatt, Schweiz ohne Verletzungen

Am 11. Juli 1987 kollidierten eine ASK 18B und eine ASW 15 nahe der Westflanke des Hasenmatt in Selzach, Schweiz. Der Pilot der ASK 18B versuchte, der herannahenden ASW 15 durch eine enge Kurve auszuweichen, aber Turbulenzen führten zu einem vorübergehenden Kontrollverlust. Der linke Flügel der ASK 18B traf den rechten Flügel der ASW 15 und trennte ein 2,5 Meter langes Stück ab. Die ASW 15 spiralte aus etwa 100 Metern Höhe abwärts, landete auf einem Baum und dann am Boden. Beide Piloten blieben unverletzt. Die ASK 18B erlitt leichte Schäden, während die ASW 15 zerstört wurde.

1. Thermaling after tow: After aerotow from Grenchen, the ASK 18B was thermaling on the west side of Hasenmatt among several other gliders in rough, locally turbulent lift.
2. Crowded soaring area: Between Grenchenberg and Weissenstein, 10–15 gliders were operating in the same general area, increasing traffic complexity and the need for separation.
3. Rough turbulent thermals: The thermals were described as irregular and rough with local medium to strong turbulence, making stable circling more difficult.
4. Tightening turn for spacing: Seeing the ASW 15 approaching from the left about 50–100 m lower, the ASK 18B pilot tightened his right-hand turn to give the other glider more room toward the slope.
5. Wing lifted and stall: As bank was increased, a gust lifted the ASK 18B’s left wing, the aircraft briefly entered an uncontrollable attitude with an aerodynamic stall and nose drop, and it rapidly lost vertical separation with the ASW 15.
6. Wing-to-wing collision: Before the ASK 18B could be fully recovered to level flight, its left wing struck the ASW 15’s right wing from behind, tearing off a 2.5 m section and sending the ASW 15 into a steep spiral from about 100 m AGL.
7. Mid-air collision: The ASW 15 crashed through a fir tree to the ground and was destroyed while the pilot was uninjured, and the ASK 18B, with minor left-wing damage, remained controllable and landed safely back at Grenchen.